Cutter blade and guide construction for a sheet material cutter with a reciprocating cantilevered blade

ABSTRACT

A sheet material cutter of the type using a reciprocating cantilevered blade includes a relatively thin reciprocating blade and a guide or sheath that surrounds the blade rearwardly of its forward cutting edge to provide extra rigidity for the blade reducing lateral and rearward deflection by the forces imposed thereon during a cutting operation. In addition to a generally vertical forward cutting edge for cutting sheet material as the blade is moved in the plane thereof, the blade also includes, at its lower end, a generally downwardly facing cutting edge permitting the blade to cut in a plunging fashion by moving it and the guide generally perpendicularly into the material being cut. The blade and guide are so constructed as to allow them to cut, during plunging movement, a slit in the sheet material equal to approximately the combined front to rear dimension of the blade and guide so that as the blade and guide are plunged into the material being cut the slit made thereby will readily accommodate the blade and the guide without seriously displacing the material or causing other problems.

Umted States Patent [151 3,682,034 Pearl [451 Aug. 8, 1972 [54] CU'I'IERBLADE AND GUIDE 3,572,202 3/1971 Gerber ..83/925 CC X CONSTRUCTION FOR ASHEET MATERIAL CUTTER WITH A Primary Examiner-Donald G. Kelly IRECIPROCATING CANTILEVERED Attorney-McCormick, Paulding & Huber BLADE[57] ABSTRACT [72] Inventor: David R. Pearl, West Hartford, I

Conn. A Sheet material cutter of the type using a reciprocatingcantilevered blade includes a relatively thin 3] Asslgnee! GerberGarment gy, 5381 reciprocating blade and a guide or sheath that sur-Hartf0rd,c0nn. rounds the blade rearwardly of its forward cutting I edgeto provide extra rigidity for the blade reducing [22] Oct 1970 lateraland rearward deflection by the forces imposed PP 77,844 thereon during acutting operation. In addition to a generally vertical forward cuttingedge for cutting sheet material as the blade is moved in the plane [52]US. Cl. ..83/635, 83/528, 88330566937, thereof, the blade also includesat its lower end, a 51 Int. Cl. ..B26d 1/06 gene'ally dwmlardly facingcutting edge F l [58] Field of Search .83/528 563 635 925 cc 697 themafia a Plungmg. mvmg 83/6l8 681 4 30/272 the guide generallyperpendicularly Into the material being cut. The blade and guide are soconstructed as to allow them to cut, during plunging movement, a slit inthe sheet material equal to approximately the com- [56] References cuedbined front to rear dimension of the blade and guide UNITED STATESPATENTS so thaglasbethe bladttel lantiguidtej arti:l plingedninto fiemater! mg cut e s it ma e ere y M rea 1y 3,585,888 6/ 197i W121i!..83/925 CCX accommodate the blade and the guide without i 32 2;3 2: 584 52 oust Ixtlisplacing the material or causing other o e 7 2,580,14612/1951 Williams ..83/697 pr 7 2,998,651 9/ 1961 Gronemeier .30/272 R 7Claim, 23 Drawing Figures PATENTEDAHI; m 3.682.034

' SHEET IN 3 DAVID R. PEARL ATTORNEYS FIG. 5

FIG. 7

76 aaw 699E)? FIG. 8

PATENTEnAuc awn 3.682.034

sum 2 or 3 9 FIG.9 4A

CUTTER BLADE AND GUIDE CONSTRUCTION FOR A SHEET MATERIAL CUTTER WITH ARECIPROCATING CANTILEVERED BLADE BACKGROUND OF THE INVENTION Thisinvention relates to cutting devices utilizing a reciprocatingcantilevered blade for cutting sheet material such as layups of fabric,and deals more particularly with the construction of a cutter blade andassociated guide for use with such a cutting device.

A cutting device of the type with which the blade and guide constructionof this invention may be employed is shown, for example, in copendingpatent application Ser. No. 821,723, filed May 5, 1969 and entitledApparatus For Cutting Sheet Material. As shown in this copendingapplication, the cutter is mounted above a table or bed which supportsthe sheet material to be cut and is moved under automatic control in theplane of the supporting surface of the bed to follow a desired line ofcut on the sheet material. The sheet material may be a layup of fabricused for making garments and the cutter may be used to cut the layupinto various desired garment pieces. The cutting blade of the cutterextends downwardly from the cutter body and passes through the materialbeing cut. When cutting along a given line the blade is reciprocatedalong a generally vertical axis while the cutteris moved forwardly alongthe line, and the forward cutting edge of the blade engages the sheetmaterial during this movement and performs the actual cutting operation.The lower end of the blade may, and preferably does, extend, at leastduring a portion of its stroke, a substantial distance below the bottomsurface of the material being. cut so as to penetrate the supportingbed, the bed being made of foamed plastic or other readily penetrablematerial.

In using a cutter of the aforedescribed type, a cutting operation may beinitiated by first positioning the cutter outside of the bounds of thematerial being cut and moving it into one edge of the material and fromsuch edge through the material to the desired line to be followed. Thisprocedure may be acceptable in many cases, but in many other cases, itis desirable to be able to begin a cut from a location located withinthe bounds of the material rather thanfrom the edge of the material. Toaccomplish this, it is necessary that the blade of the cutter be capableof making what is referred to as a plunging or stabbing type of cut. Ina plunging or stabbing type of cut, the cutter is first moved to araised position at which the cutter blade is located throughout the fullextent of its reciprocating stroke above the top surface of the materialto be cut. The cutter is then held stationary in the plane of thematerial and while so held is moved downwardly to plunge or stab theblade thereof downwardly through the material, the blade during thisplunging or stabbing motion being reciprocated. After the blade is fullyplunged through the material it is then moved forwardly along thedesired line of cut to cut the material along such line. Alternatively,a plunging or stabbing type of cut may be used by itself to form markingslits or the like in the material.

In reciprocating cantilevered blade type cutters, the cutter blade issupported from only one of its ends and in order to minimize lateral andrearward deflection of the blade, it is known to use a stationary sheathor guide with the blade which surrounds the blade except for an exposedforward cutting edge portion. Such sheaths or guides are relativelyeffective in cases where the cutter is not used to perform stabbing orplunging type of cuts. When such stabbing or plunging type of cuts areused, however, the sheath or guide tends to interfere with such a cutinsofar as the cut made by the blade is of insufficient size toaccommodate both the blade and the guide. To reduce this problem, theguide may be made of a smaller size but this then reduces itseffectiveness in restraining lateral and rearward deflection.

The general object of this invention is, therefore, to provide a bladeand guide construction for a sheet material cutter of the foregoingcharacter which blade and guide construction is such as to enable theblade to readily execute plunging or stabbing types of cuts with theguide nevertheless providing a high degree of rigidiconstruction for useas part of a sheet material cutter utilizing a cantileveredreciprocating cutter blade. The

lateral and rearward cutter blade is elongated and has a cutting edgeextending along its forward edge portion and also a cutting edge at itslower end portion facing generally downwardly, assuming that thematerial to be cut is laid out horizontally and the main body of thecutter located above such material. The guide used with the blade has arecess for receiving the blade and provides the guide with two cheeks onopposite sides of the recess each of which engages a respective one ofthe side faces of the blade. At the base of the recess is a forwardlyfacing surface which engages the rear edge of the blade to preventrearward deflection thereof. At the lower end of the blade and guideeither the blade has a rearwardly extending hook portion which carriesthe downwardly facing edge of the blade rearwardly to the rear limit ofthe guide or the guide has a sharpened rear edge which in combinationwith the downwardly facing edge of the blade forms a composite cuttingedge having a front to rear length equal to the combined front to reardimension of the blade and guide.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary perspectiveview of a cutter utilizing a cutter blade and guide constructed inaccordance with the present invention.

FIG. 2 is an enlarged side elevational view of the cutter and guide ofFIG. 1 with portions of the guide being shown broken away to betterreveal the shape of the blade.

FIG. 3 is a horizontal sectional view taken on the line 3-3 of FIG. 2.

FIG. 4 is a horizontal sectional view taken on the line 4-4 of FIG. 2.

FIG. 5 is a rear elevational view of the blade and guide of FIG. 2.

FIG. 6 is a side elevational view of the lower end of a blade and guidecomprising an alternative embodiment of this invention.

FIG. 7 is a horizontal sectional view taken on the line 77 of FIG. '6.

FIG. 8 is a side elevational view of a blade and guide comprising analternative embodiment of this invention with portions of the guidebeing shown broken away to better reveal the shape of the blade.

FIG. 9 is a horizontal sectional view taken on the line 9-9 of FIG. 8.

FIG. 10 is a horizontal sectional view taken on the line10-10 of FIG. 8.

FIG. 11 is a rear elevational view of the blade and guide of FIG. 8.

FIG. 12 is a side elevational view of the lower end of a blade and guidecomprising an alternative embodiment of this invention.

FIG. 13 is a horizontal sectional view taken on the line 13-13 of FIG.12.

FIG. 14 is a horizontal sectional view taken on the line 14l4 of FIG.12.

FIG. 15 is a horizontal sectional view taken on the line 1515 of FIG.12.

- FIG. 16 is a horizontal sectional view taken on the line 16-16 of FIG.12.

FIG. 17 is a rear elevational view of the blade and guide of FIG. 12.

FIG. 18 is a side elevational view of the lower end of a blade and guidecomprising another alternative embodirnent of this invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS FIG. 1 shows a sheet materialcutter utilizing a blade and guide constructed in accordance with thisinvention. Referring to this figure, the cutter is indicated generallyat 20, and includes a cutter head 22, a cutter blade 24, a cutter bladeguide 26 and a presser foot 28. The various parts of the cutter areshown in an operative cutting relationship with a piece of sheetmaterial 30 to be cut. The sheet material 30 may, as illustrated,comprise a layup of a large number of individual layers of fabric and issupported by a supporting bed 32 having an upwardly facing supportingsurface 34. The material of which the supporting bed 32 is made is of apenetrable nature, such as a foamed plastic, so that the lower end ofthe cutter blade 24 may penetrate it by passing through the supportingsurface 34 during the cutting operation.

During the normal cutting operation illustrated in FIG. 1, the cutterblade 24 is reciprocated vertically while at the same time the cutter 20is moved in the plane of the material 30 to follow a desired line ofcut. Such movement along a desired line of cut may be antomaticallycontrolled and for this purpose the cutter 20 is mounted on a supportingcarriage 36 which in turn is supported for controlled movement in bothof the illustrated X and Y coordinate directions. During a normalcutting operation, the presser foot 28 engages the top surface of thematerial 30 to prevent the material from moving upwardly during theupstroke of the blade 24, and from its illustrated position the entirecutter 20 may be moved upwardly relatively to the carriage 36 to a pointat which the blade 24 and its as sociated guide 26 are raised above thetop surface of the material 30. Similarly, from its raised position, theentire cutter 20 may be moved vertically downwardly while the carriage36 is held stationary in order to move the blade 24 and its guide 26downwardly through the material 30 in a plunging or stabbing type ofcut, the blade 24 being reciprocated during such downward stabbing orplunging movement.

Turning now to FIGS. 2 to 5 for a more detailed description of the blade24 and its associated guide 26, FIG. 2 shows the blade and guide in sideelevational view with part of the guide being broken away to betterreveal the shape of the blade and the guide recess which receives theblade. In this figure, the solid lines show theblade in the raised limitof its reciprocating stroke and the broken lines show the blade in thelower limit of its stroke. Considering FIGS. 2 to 5, the blade 24 has anupper end portion 38 which is adapted to be attached to a chuck or otherdriving means of the cutter head 22 for reciprocating it verticallybetween its illustrated solid line and broken line positions. At thelower end of the blade is a lower end portion 40 and between the upperand lower end portions 38 and 40 is an intermediate portion 42. Theblade is of an elongated shape and is made from a relatively thin flatstock. Along its forward edge it is sharpened to provide a forwardlyfacing cutting edge 44 which extends vertically or longitudinally of theblade along a substantial portion of its length. The lower end portionof the blade is shaped to provide two generally downwardly facing edges46 and 48, both of which are sharpened and meet at a point 50. The edge46 is inclined and extends upward and forwardly from the point 50 to theedge 44, and the edge 48 is inclined and extends upwardly and rearwardlyfrom the point 50 to the rear limit of the lower end portion of theblade. In its front to rear dimension, the lower end portion of theblade has a dimension greater than its intermediate portion 42 andincludes a part 52, referred to as a hook portion, which extendsrearwardly beyond the rear edge 54 of the intermediate portion 42.

The guide 26 which receives the blade 24 has a longitudinally extendingrecess 56 which receives the rear portion of the blade so that the guidesurrounds a substantial portion of the blade leaving its forward edgeportion exposed for cutting. As shown best in FIGS. 3 and 4, the recess56 defines two cheeks 58, 58 located on opposite sides of the blade 24which engage the side faces of the blade and thereby provide it withaddiportion of the blade to provide space for accommodating the fullfront to rear dimension of the lower end portion. More particularly, atthe lower end of the guide the recess 56 extends through the full frontto rear dimension of the guide, and the hook portion 52 of the bladeextends rearwardly to a point aligned with the rear edge 59 of theguide. As a consequence of this, the horizontal length component of thetwo downwardly facing cutting edges 46 and 48, taken in combination, isequal to the full front to rear dimension of the combined blade andguide.

From the foregoing, it will therefore be understood that in theconstruction illustrated in FIGS. 2 to 5, the guide 26 engages the bladeon both sides thereof along substantially its entire length to restrainit against lateral deflection. It, also, along the intermediate portionof the blade, extends along the rear edge thereof and by engagementtherewith restrains it against rearward deflection. Further, by virtueof the fact that the generally downwardly facing cutting edges 46 and 48have a combined horizontal length component equal to the front to reardimension of the combined blade and guide, the slit cut by such edges.as the blade is moved in a plunging motion through the material beingcut is sufficiently long in its front to rear dimension to receive theblade and the guide. As shown in FIG. 5, the lower end of the guide 26is preferably feathered as indicated at 60, 60 so as to gradually blendwith the side faces of the blade thereby allowing the guide to smoothlyenter the slit cut by the blade as it is plunged through the materialbeing cut.

It should also be noted from FIG. 2 that at the lower end of the blade,the point 50 is located closer to the rear limit of the blade than tothe front limit. This is done so that as the blade and guide are movedin a plunging fashion through the material to be cut, the horizontalcomponent of the force imposed by the material on the forward edge 46will be. somewhat greater than the horizontal component of the forceimposed by the material on the edge 48. Therefore, the resultant of suchhorizontal components will be a horizontal force tending to move theblade rearwardly against the base of the recess 56. If the resultantforce were directed in the other direction, it would tend to move thelower end of the blade forwardly relative to the guide 26, or out of therecess 56, which would be an undesirable condition. It should of coursebe understood that the shape of the cutting edge or edges provided atthe lower end of the blade may vary considerably from that shown, and insome instances, for example, the lower end of the blade may include onlyone generally downwardly facing cutting edge preferably inclineddownwardly and rearwardly from the forward cutting edge 44, as forexample in the construction of FIG. 22 hereinafter discussed. Also, inthe blade 24 illustrated in FIG. 2, the hook portion 52 terminates at apoint aligned with the rear edge 59 of the guide, but if desired, thishook portion may, in some instances, be made to extend a slight distancerearwardly beyond the rear guide edge 58 so that the slit made by theknife during a plunging cut is slightly greater than the front to reardimension of the combined blade and guide as measured at a point alongthe intermediate portion of the blade.

Also, it is not necessary in all instances to carry the guide 26 belowthe intermediate portion 42 of the blade. By way of example, FIGS. 6 and7 illustrate one construction of a blade and guide which issubstantially identical to the construction of FIGS. 1 to 5 except forthe manner in which the guide is terminated at its lower end. In FIGS. 6and 7, the blade is indicated at 62 and the associated guide at 64. Theblade 62 has a forward vertical cutting edge 66, and at its lower endincludes two generally downwardly facing cutting edges 68 and 70, thelower end of the blade also including a rearwardly extending hookportion 72. The guide 64 includes a recess 74 which receives the blade62, and the intermediate portion 63 of the blade has a rear edge 76which engages the base of the recess 74 to prevent rearward deflectionof the blade.

In FIG. 6, the solid lines show the blade in the upper limit of itsstroke, and the broken line show it in the lower limit of its stroke.From this figure, it will be noted that the guide 64 is so shaped thatits lower end 78 is located slightly above the hook portion 72 when theblade is in the upper limit of its stroke, and preferably the lower end78 is shaped so as to have a sharpened or rounded edge giving it athickness, rearwardly of the rear blade edge 76, no greater than thethickness of the blade, the cheeks of the guide also being feathered attheir lower ends to smoothly blend with the sides of the blade.Similarly to the construction of FIGS. 1 to 5, the blade edges 68 and 70of the FIG. 6 and 7 construction meet at a point 69 located closer tothe rear limit of the blade than to the front limit. They also have acombined horizontal length component equal to the combined front to reardimension of the blade and guide so that the slit made during a plungingoperating has a length sufficient to readily accommodate the blade andthe guide as they are moved downwardly through the material being cut.

FIGS. 8 to 11 show another alternate construction of a blade and guideembodying this invention. In these figures the blade is indicated at 80and the guide at 82. The solid lines show the blade in the upper limitof its reciprocating movement and the broken lines show it in the lowerlimit of its reciprocating movement. The blade is of a substantiallyuniform front to rear dimension along the major portion of its lengthand at its upper end is adapted for attachment to a chuck or other drivemeans of the cutter head for reciprocating it vertically between thesolid and broken line positions. Its vertical forward edge 84 issharpened for cutting a sheet material during a normal cutting operationas the cutter head is moved in the plane of the sheet material to causethe blade and guide to follow along a desired line of cut. The lower endof the blade 80 is shaped generally similarly to the lower end of theblade 24 of FIG. 2 to include two generally downwardly facing cuttingedges 86 and 88 which meet at a point 90. The cutting edge 86 isinclined upwardly and forwardly from the edge 90 and the edge 88 isinclined upwardly and rearwardly from the point 90, the point 90 beinglocated closer to the rear edge 92 of the blade than to the front edge84 so that the resultant of the horizontal forces applied to the cuttingedges 86 and 88 is a horizontal force urging the blade rearwardly towardthe guide 82.

The guide 82 includes a recess 94 for receiving the blade 80 with theforward portion thereof projecting forwardly beyond the guide, the guidehaving two cheeks 96, 96 located on opposite sides of the blade forrestraining the blade against lateral deflection and the base of therecess 94 being engagable with. the rear edge 92 of the blade torestrain the blade against rearward deflection. As will be best notedfrom FIG. 8 the guide 82 extends rearwardly beyond the rear edge 92 ofthe blade so that the combined front to rear dimension of the blade andguide is slightly greater than the maximum front to rear dimension ofthe blade taken by itself. Therefore, in order to make a slit ofsufiicient length to accommodate both the blade and the guide during aplunging movement through the material being cut, the lower end of theguide 82 is sharpened, as indicated at 98, so that it will also cut thesheet material as it is pushed therethrough. That is, the cutting edges86 and 88 of the blade 80 working in combination with each other andwith the edge 98, during a plunging movement of the blade and guide, cuta slit in the material equal to the full front to rear dimension of theblade and guide to cause the slit to be of an adequate size to receivethe blade and guide as both elements are pushed therethrough.

FIGS. 12-17 show another alternate construction of a blade and guideembodying this invention and which construction is generally similar tothat of FIGS. 8-11 except for the manner in which a sharp edge isapplied to the lower end of the guide rearwardly of the blade forcutting a portion of the slit as the blade and guide are plunged intothe sheet material being cut. Therefore, in these figures variousfeatures which are substantially similar to those of FIGS. 8-11 havebeen given the same reference numerals and need not be furtherdescribed. As to the differences between the guide of FIG. 12 and thatof FIG. 8, the guide in FIG. 12 is indicated at 100 and includes, at itslower end, a downwardly directed extension 102 which is shaped toprovide a generally horizontally extending downwardly facing cuttingedge 104. The extension 102 is also preferably shaped, as shown insectional views and 16, to provide sharp edges 106 and 108 along itsfront and rear vertical sides, respectively. The edge 106, locatedbetween the rear edge 92 of the blade and the extension 102, serves tocut off any threads which may become lodged between the blade and theextension, and the edge 108 aides in assuring that the slit made by theknife edges 86 and 88 and the guide edge 104 has a length equal to thefull front to rear dimension of the blade and guide.

FIGS. 18 and 19 show another alternate construction of a blade and guideembodying this invention and which construction is basically similar tothat of FIGS. 12-17 except for the extension 102 of FIG. 12 beingreplaced by an insert 110 which is brazed or otherwise fastened to theremainder of the guide, indicated at 112. This allows the guide to bemade of a stiff wear resistant material such as tungsten carbide and theinsert to be made of another material, such as hard steel, moreadaptable to providing a sharpened edge. The insert 110 has a point 114and a curved sharpened edge 116 which extends generally upwardly andforwardly from the point 114 to the rear edge 92 of the blade. It alsoincludes a generally vertical sharpened rear edge 118 which may, asshown, extend rearwardly a slight distance beyond the rear edge of theguide.

FIGS. and 21 show still another alternative construction of a blade andguide embodying this invention, and in which construction the blade andguide are made to have a self-sharpening action on at least a portion ofthe downwardly facing edge or edges of the blade. In these figtres, theblade is indicated at 120 and in addition to including a verticalforward edge 122 includes two generally downwardly facing edges 124 and126. As shown best in FIG. 21 the two edges 124 and 126 are both made bybeveling the blade 120, as indicated at 128, from one side only with theother side 129 of the blade being flat all the way to the edges 126 and124.

The guide of FIGS. 20 and 21 is indicated at 130 and at its lower endincludes an extension 132 located adjacent the flat side 129 of theblade. The extension 132 is sharpened to provide a cutting edge 134located directly adjacent the flat side 129 of the blade. A portion ofthe extension 132 extends rearwardly beyond the rear edge of the bladeand has a point 136 which aids in piercing the material being cut duringa plunging operation. Along the portion of the extension which extendsrearwardly beyond the blade the sharp edge 134 acts to cut the materialduring a plunging motion, and forwardly of the rear edge of the bladethe edge 134 wipes over the edge 126 and part of the edge 124 of theblade as the blade is reciprocated and thereby produces aself-sharpening action on itself and the edges 124 and 126.

FIGS. 22 and 23 show another alternative construction of a blade andguide embodying this invention, and which construction also includesself-sharpening of the blade lip. In the construction of these figuresthe blade is indicated at 138 and the guide at 139. The blade 138 has avertically extending forward cutting edge 140 and a single generallydownwardly directed cutting edge 142 at its lower end, the edge 142being inclined slightly upwardly and forwardly from a point 144 formedby the intersection of it with the rear edge 146 of the blade. The edgev142 is formed by a single bevel 148 on one side of the blade, the otherside of the blade, the right hand side in FIG. 23, being flat andunbevelled.

The guide 139 of FIGS. 22 and 23 is a composite member comprised of twocheek pieces or sides 150, 150 preferably made of tungsten carbide orother wear resistent material, a spacer 152, which may be made of thesame material as the cheek pieces 150, 150 and an intermediate member154 made of steel or other material adapted to provide a good cuttingedge. The parts 150, 150, 152 and 154 are preferably brazed together.The spacer 152 extends from the rear edge of the guide to the rear edgeof the blade and defines the bottom of the recess of the guide. Theintermediate member 154 overlies the inside face of the right hand cheekpiece 150 of FIG. 23 and at its lower end extends beyond the cheekpieces 150, 150 to provide a sharpened extension 156. The extension 156is shaped to provide a piercing point 158 and two sharpened edges 160and 162. The two edges 160 and 162 are each formed by a single bevel,such as that shown at .164 in FIG. 23, on the right-hand side of theextension, the left-hand side of the extension being flat andunbevelled.

In the FIG. 22 the broken lines show the blade 138 in the lower extentof its reciprocating movement and the solid lines show it in the upperextent of such movement, and it will be noted that the lower edge 142 ofthe blade does not extend below the point 158 of the piercing extension.Therefore, as the blade and guide are moved ,in a plunging fashionthrough a piece of material to be cut the edges 160 and 162 of theextension 156 cut the major portion of the slit with the forward part ofthe edge 142 of the blade cutting a minor portion of such slot. Also, itwill be understood that as the blade is moved in its reciprocatingmotion the rubbing between it and the extension 156 will cause theextension to have a self-sharpening effect on the major portion of theedge 142.

I claim:

1. A cutter blade and associated guide for use as'part of a sheetmaterial cutter utilizing a cantilevered reciprocating cutter blade,said cutter blade being elongated and having an upper end portionadapted for attachment to a driving means of a cutter such as aforesaidfor reciprocating it along its longitudinal axis, said cutter bladehaving two side faces and a forward cutting edge extendinglongitudinally thereof, said guide extending longitudinally of saidblade along at least a portion thereof and having a longitudinallyextending forwardly opening recess for receiving said blade with saidforward cutting edge projecting therefrom, said guide having two cheekslocated respectively on opposite sides of said recess and engageablerespectively with said two side faces of said cutter blade to restrainit against lateral deflection, said guide also having a forwardly facingsurface at the base of said recess engageable with said blade torestrain it against rearward deflection, and means at the lower end ofsaid blade and guide defining at least one generally downwardly facingcutting edge for cutting in a piece of sheet material as said blade andguide are plunged downwardly therethrough a slit having a lengthsubstantially no less than the combined front to rear dimension of saidblade and guide, said guide having a lower end portion including adownwardly extending extension located entirely to the rear of andadjacent the rear edge of said blade, and said means defining at leastone generally downwardly facing cutting edge including a generallydownwardly facing cutting edge on the lower end portion of said bladeand a generally downwardly facing sharp edge of said extension having afront to rear length component equal to the front to rear length of saidextension. Y

2. A cutter blade and associated guide for use as part of a sheetmaterial cutter utilizing a cantilevered reciprocating cutter blade,said cutter blade being elongated and having an upper end portionadapted for attachment to a driving means of a cutter such as aforesaidfor reciprocating it along its longitudinal axis, said cutter bladehaving two side faces and a forward cutting edge extendinglongitudinally thereof, said guide extending longitudinally of saidblade along at least a portion thereof and having a longitudinallyextending forwardly opening recess for receiving said blade with saidforward cutting edge projecting therefrom, said guide having two cheekslocated respectively on opposite sides of said recess and engageablerespectively with said two side faces of said 235%%l?%5?&&2&llfi .33'fiis of said recess engageable with said blade to restrain it againstrearward deflection, and means at the lower end of said blade and guidedefining at least one generally downwardly facing cutting edge forcutting in a piece of sheet material as said blade and guide are plungeddownwardly therethrough a slit having a length substantially no lessthan the combined front to rear dimension of said blade and guide, oneof said two cheeks of said guide at its lower end extending downwardlybeyond the other of said cheeks, and said means defining at least onegenerally downwardly facing cutting edge at said lower end of said bladeand guide comprising at least one cutting edge on the lower end portionof said blade which cutting edge is defined by a single bevel on theside of said blade opposite the side thereof which engages said onecheek so as said cutting edge is moved past the lower end of said cheekduring its reciprocating movement the rubbing action between said onecheck and said blade imposes a selfsharpening effect on said at leastone cutting edge on the lower end portion of said blade.

3. A cutter blade and associated guide as defined in claim 1 furthercharacterized by said generally downwardly facing edge of said extensionbeing oriented generally horizontally, and said extension including twoother sharp edges one of which extends vertically along its forward edgeand the other of which extends vertically along its rear edge.

4. A cutter blade and associated guide as defined in claim 1 furthercharacterized by said extension having a sharpened vertically extendingrear edge which rear edge is located slightly rearwardly beyond the rearlimit of the remainder of said guide.

5. A cutter blade and associated guide as defined in claim 1 furthercharacterized by said extension being an insert fixed to the remainderof said guide and made of a material different from that of saidremainder of said guide.

6. A cutter blade and associated guide as defined in claim 2 furthercharacterized by said one cheek having a generally downwardly facingcutting edge formed on the lower end thereof.

7. A cutter blade and associated guide as defined in claim 6 furthercharacterized by said one cheek of said guide at its lower end extendingrearwardly beyond the

1. A cutter blade and associated guide for use as part of a sheetmaterial cutter utilizing a cantilevered reciprocating cutter blade,said cutter blade being elongated and having an upper end portionadapted for attachment to a driving means of a cutter such as aforesaidfor reciprocating it along its longitudinal axis, said cutter bladehaving two side faces and a forward cutting edge extendinglongitudinally thereof, said guide extending longitudinally of saidblade along at least a portion thereof and having a longitudinallyextending forwardly opening recess for receiving said blade with saidforward cutting edge projecting therefrom, said guide having two cheekslocated respectively on opposite sides of said recess and engageablerespectively with said two side faces of said cutter blade to restrainit against lateral deflection, said guide also having a forwardly facingsurface at the base of said recess engageable with said blade torestrain it against rearward deflection, and means at the lower end ofsaid blade and guide defining at least one generally downwardly facingcutting edge for cutting in a piece of sheet material as said blade andguide are plunged downwardly therethrough a slit having a lengthsubstantially no less than the combined front to rear dimension of saidblade and guide, said guide having a lower end portion including adownwardly extending extension located entirely to the rear of andadjacent the rear edge of said blade, and said means defining at leastone generally downwardly facing cutting edge including a generallydownwardly facing cutting edge on the lower end portion of said bladeand a generally downwardly facing sharp edge of said extension having afront to rear length component equal to the front to rear length of saidextension.
 2. A cutter blade and associated guide for use as part of asheet material cutter utilizing a cantilevered reciprocating cutterblade, said cutter blade being elongated and having an upper end portionadapted for attachment to a driving means of a cutter such as aforesaidfor reciprocating it along its longitudinal axis, said cutter bladehaving two side faces and a forward cutting edge extendinglongitudinally thereof, said guide extending longitudinally of saidblade along at least a portion thereof and having a longitudinallyextending forwardly opening recess for receiving said blade with saidforward cutting edge projecting therefrom, said guide having two cheekslocated respectively on opposite sides of said recess and engageablerespectively with said two side faces of said cutter blade to restrainit against lateral deflection, said guide also having a forwardly facingsurface at the base of said recess engageable with said blade torestrain it against rearward deflection, and means at the lower end ofsaid blade and guide defining at least one generally downwardly facingcutting edge for cutting in a piece of sheet material as said blade andguide are plunged Downwardly therethrough a slit having a lengthsubstantially no less than the combined front to rear dimension of saidblade and guide, one of said two cheeks of said guide at its lower endextending downwardly beyond the other of said cheeks, and said meansdefining at least one generally downwardly facing cutting edge at saidlower end of said blade and guide comprising at least one cutting edgeon the lower end portion of said blade which cutting edge is defined bya single bevel on the side of said blade opposite the side thereof whichengages said one cheek so as said cutting edge is moved past the lowerend of said cheek during its reciprocating movement the rubbing actionbetween said one cheek and said blade imposes a self-sharpening effecton said at least one cutting edge on the lower end portion of saidblade.
 3. A cutter blade and associated guide as defined in claim 1further characterized by said generally downwardly facing edge of saidextension being oriented generally horizontally, and said extensionincluding two other sharp edges one of which extends vertically alongits forward edge and the other of which extends vertically along itsrear edge.
 4. A cutter blade and associated guide as defined in claim 1further characterized by said extension having a sharpened verticallyextending rear edge which rear edge is located slightly rearwardlybeyond the rear limit of the remainder of said guide.
 5. A cutter bladeand associated guide as defined in claim 1 further characterized by saidextension being an insert fixed to the remainder of said guide and madeof a material different from that of said remainder of said guide.
 6. Acutter blade and associated guide as defined in claim 2 furthercharacterized by said one cheek having a generally downwardly facingcutting edge formed on the lower end thereof.
 7. A cutter blade andassociated guide as defined in claim 6 further characterized by said onecheek of said guide at its lower end extending rearwardly beyond therear limit of said blade and said edge on said lower end of said onecheek also extending rearwardly beyond said blade.